1. Field of the Invention
This invention relates to a universal joint and a yoke therefor for a steering apparatus incorporated in the steering apparatus of an automobile and transmitting the movement of a steering shaft to a steering gear.
2. Related Background Art
The steering apparatus of an automobile is constructed as shown, for example, in FIG. 11 of the accompanying drawings. The movement of a steering wheel 1 is transmitted to a steering gear 4 through a steering shaft 2 and a connecting shaft 3, and the wheels are steered by the steering gear 4. It is often the case that the steering shaft 2 and the input shaft 5 of the steering gear 4 cannot be provided on the same straight line. Therefore, heretofore, the connecting shaft 3 has been provided between the shafts 2 and 5, and the opposite end portions of this connecting shaft 3 and the end portions of the steering shaft 2 and the input shaft 5 have been coupled together through universal joints 6 and 6 so that power transmission can be effected between the steering shaft 2 and the input shaft 5 which are not on the same straight line.
The universal joint 6 incorporated in such a power transmitting mechanism or the like has heretofore been comprised of first and second yokes 7 and 8 each formed into a bifurcated shape, and a cruciform shaft or spider 9 for displaceably coupling the yokes 7 and 8 together, as shown in FIG. 12 of the accompanying drawings. In the case of the universal joint shown in FIG. 12, the yokes are made by pressing a metallic plate. In Japanese Patent Application Laid-Open No. 3-41220, there is described a yoke as shown in FIGS. 13-14 and 15-16 of the accompanying drawings. Each of the yokes 10 described in the above-mentioned publication is constructed by fitting a coupling member 11 and a coupling arm 12 to each other, and welding them to each other.
The coupling member 11 is made into a tubular shape by press-shaping a metallic plate having sufficient rigidity, such as a carbon steel plate, and has a split 13 formed in a circumferential portion thereof and serrate grooves 14 formed in the inner peripheral surface thereof. Also, on one end portion (the left end portion as viewed in FIGS. 13 and 15) of the coupling member 11, a pair of flange portions 15 and 16 are provided integrally with the coupling member 11 with the split 13 interposed therebetween. These flange portions 15 and 16 are made thicker by gathering portions of the metallic plate constituting the coupling member 11 (the case of FIGS. 13-14) or by turning back a portion of the metallic plate by 180.degree. (the case of FIGS. 15-16). One flange portion 15 (on the left as viewed in FIGS. 14 and 16) is formed with a threaded hole 17 and the other flange portion 15 (on the right as viewed in FIGS. 14 and 16) is formed with a through-hole 18. The threaded hole 17 and the through-hole 18 are formed coaxially with each other, and the inner diameter of the through-hole 18 is made sufficiently larger than the inner diameter of the threaded hole 17, whereby the fore end portion of a bolt inserted in the through-hole 18 is threadably engageable with the threaded hole 17.
The coupling arm 12 is also made by press-shaping a metallic plate having sufficient rigidity, such as a carbon steel, into a U-shape. The base portion of this coupling arm 12 is formed with a through-hole 19 and the opposite end portions of the coupling arm 12 are formed with coaxial circular holes 20 and 20, respectively.
Regarding the assembly of the coupling member 11 and coupling arm 12 constructed as described above, the other end portion (the right end portion as viewed in FIGS. 13 and 15) of the coupling member 11 is fitted in the through-hole 19 formed in the base portion of the coupling arm 12 and also, the outer peripheral surface of the other end portion of the coupling member 11 and the marginal edge portion of the through-hole 19 in the base portion of the coupling arm 12 are welded to each other thereby providing a yoke 10 for the universal joint. When such a yoke 10 is to be assembled to the universal joint and the end portion of the connecting shaft 3 (FIG. 11) is to be coupled to the yoke 10, a serrate portion formed on the end portion of the connecting shaft 3 is inserted into the coupling member 11, whereafter a bolt is inserted from the right, as viewed in FIGS. 14 and 16, into the through-hole 18 formed in the flange portion 16 and is threadably engaged with the threaded hole 17 formed in the flange portion 15, and is fastened. As a result, the yoke 10 and the end portion of the connecting shaft 3 are firmly coupled together.
Now, in order to alleviate a shock applied to a driver's body when, during a collision, the driver's body collides with the steering wheel 1, various safety mechanisms have been considered, including giving a shock alleviating capability to the universal joint portion. In order to meet such requirement, it has been considered to connect metallic bellows between the coupling member 11 and the coupling arm 12 in series with the two members 11 and 12 to give a shock alleviating capability to the universal joint including the yoke 10 shown in FIGS. 13 and 15.
That is, one end portion of the bellows is coupled to the outer peripheral surface of the other end portion of the coupling member 11 and the other end portion of the bellows is coupled to the base end portion of the coupling arm 12, both by welding. Under normal conditions, the bellows effects the transmission of a rotational force between the coupling member 11 and the coupling arm 12 to thereby make steering possible. In contrast, when an impact force in a direction of compression in the axial direction of the yoke is applied during a collision, the bellows is crushed to thereby prevent any change in the inclination of the steering wheel or the pressure from below the steering wheel, thus alleviating the shock applied to the driver's body.
However, when a metallic bellows is simply incorporated in the prior-art structure as shown in FIGS. 13 and 15, it is difficult to achieve both durability of the yoke and shock absorbing capability. That is, the yoke 10 constituting the universal joint for the steering apparatus is small and therefore the outer diameter of the coupling member 11 also is small. For this reason, when the metallic bellows is simply incorporated in the prior-art structure as shown in FIGS. 13 and 15, the diameter of the bellows also becomes small.
Under normal conditions, the bellows is subjected to stress in the direction of rotation each time the steering wheel 1 is operated and therefore, when the diameter thereof is small, internal strain becomes great and sufficient durability cannot be obtained. Of course, if the thickness of the bellows is made great, it will be possible to obtain durability, but it will become difficult for the bellows to be crushed on the occasion of a collision and shock absorbing capability will become insufficient. If the diameter of the bellows is made large without the thickness thereof being made great, sufficient durability and shock absorbing capability could be obtained. Therefore, it would be possible, for example, to fit and fix a cylindrical spacer to the end portion of the coupling member 11 and fit the end portion of the bellows to the outer peripheral surface of this spacer to thereby make the diameter of the bellows larger. However, the use of such a spacer means an increase in the number of parts and also leads to the cumbersomeness of the manufacture of parts, the custody of the parts and the assembling work, which in turn leads to an increase in the costs of the yoke with the bellows and the universal joint incorporating the yoke therein.